1. Technical Field
The present invention relates to an actuator device including piezoelectric elements displaceably provided on a substrate. The invention also relates to a liquid-jet head and a liquid-jet apparatus provided with the actuator device as liquid jetting means for jetting liquid from nozzle orifices.
2. Related Art
As a piezoelectric element used for an actuator device, there is one constituted by interposing, between an upper electrode and a lower electrode, a piezoelectric layer made of a piezoelectric material exhibiting an electromechanical transduction function. An example of such piezoelectric materials is crystallized piezoelectric ceramic. Such an actuator device is generally called an actuator device of flexure vibration mode, and is used by being mounted on a liquid-jet head or the like. Representative examples of the liquid-jet head include an ink-jet recording head in which a part of each pressure-generating chamber communicating with a nozzle orifice that ejects ink droplets is composed of a vibration plate. This vibration plate is deformed by a piezoelectric element to apply pressure to ink in the pressure-generating chamber, and thereby ink droplets are ejected from a nozzle orifice. On the other hand, in an actuator device mounted on the ink-jet recording head, the piezoelectric elements are formed to be independent of one another, and are provided to the pressure-generating chambers, respectively. For this purpose, firstly, a uniform piezoelectric material layer is formed all over an entire surface of the vibration plate by a deposition technique, and then the piezoelectric material layer into shapes corresponding to the respective pressure-generating chambers by a lithography method. See, for example, JP-A-2003-127366 (pp. 4 to 7, and FIGS. 1 to 4).
In the configuration of JP-A-2003-127366, however, the longitudinal end portions of each piezoelectric active portion which is the substantial driver of the piezoelectric element is defined by end portions of the lower electrode. This configuration causes a problem. The piezoelectric layer is destroyed by electric field concentration that occurs in these end portions of the lower electrode.
Additionally, the piezoelectric layer as described above is formed, for example, in the following manner. A lower electrode is formed on a substrate by patterning the lower electrode, and then the piezoelectric layer is formed over the lower electrode by a sol-gel method or by a metal organic decomposition (MOD) method. When such a way of forming the piezoelectric layer in which the piezoelectric layer is formed after patterning the lower electrode there are problems. The crystal grain size of the piezoelectric layer (a dielectric material) becomes large, and degradation in crystallinity takes place as voids (air gaps) are formed. Another problem is that no piezoelectric layer with a uniform film thickness is obtained because of the steps formed in the lower electrode.
Additionally, when the piezoelectric layer is formed through crystallization by baking, the lower electrode and the substrate (an elastic film), existing as base materials of the piezoelectric layer, cause an error in the heating temperature for heating the piezoelectric layer. The error derives from the difference in the heat absorption between the substrate (the elastic film) and the lower electrode. By such an error in the heating temperature, the crystallinity of the piezoelectric layer formed in regions facing the end portions of the lower electrode is degraded, and there arises a problem. No piezoelectric layer with uniform crystallinity in a plane direction cannot be obtained. Moreover, there arises a problem, due to these problems in manufacturing the piezoelectric layer, and due to the above-mentioned electric field concentration, when the piezoelectric elements are driven. The piezoelectric layer in the regions facing the end portions of the lower electrode is destroyed.
Another actuator device is proposed, for example, in JP-A-2000-263785 (pp. 4 to 6, and FIGS. 1 and 2). In the actuator device, the end portions of the upper electrode are formed to be in inner positions than the end portions of the lower electrode. Each of piezoelectric active portions, which are the substantial drivers of the respective piezoelectric elements, has its longitudinal end portions defined by the longitudinal end portions of the upper electrode.
The configuration of JP-A-2000-263785, however, has a problem. The piezoelectric layer is destroyed by electric field concentration occurring in the end portions of the upper electrode.
Additionally, a voltage is applied between the lower electrode and the extension wiring that extends from one end portion of the upper electrode onto a substrate. Thus, the piezoelectric layer outside the end portions of the upper electrode is also driven. Consequently, there arises a problem. The end portions of the upper electrode cannot define the longitudinal end portions of each piezoelectric active portion.
The extension wiring provided from the upper electrode causes another problem. A short circuit becomes more likely to occur between the extension wiring and each of the end portions of the lower electrode.
It should be noted that these problems exist not only with a manufacturing method of an actuator device used for an ink-jet recording head, but also with a manufacturing method of an actuator device used for a liquid-jet head which ejects liquid other than ink.